1. Field of the Invention
This invention relates to novel inhibitors of mitotic kinesins, in particular the mitotic kinesin KSP, and pharmaceutical compositions containing the inhibitors. The compounds of this invention are useful for the treatment of cellular proliferative diseases, for example cancer, hyperplasias, restenosis, cardiac hypertrophy, immune disorders, fungal infections and inflammation. This invention also provides methods for preparing these inhibitors.
2. Description of the State of the Art
Among the therapeutic agents used to treat cancer are the taxanes and vinca alkaloids, which act on microtubules. Microtubules are the primary structural elements of the mitotic spindle, which is responsible for distribution of replicate copies of the genome to each of the two daughter cells that result from cell division. It is presumed that disruption of the mitotic spindle by these drugs results in inhibition of cancer cell division and induction of cancer cell death. However, microtubules form other types of cellular structures, including tracks for intracellular transport in nerve processes. Because drugs such as taxanes and vinca alkaloids do not specifically target mitotic spindles, they have side effects that limit their usefulness.
Improvements in the specificity of agents used to treat cancer is of considerable interest, in part because of the improved therapeutic benefits which would be realized if the side effects associated with administration of these agents could be reduced. Traditionally, dramatic improvements in the treatment of cancer have been associated with identification of therapeutic agents acting through novel mechanisms. Examples include not only the taxanes, but also the camptothecin class of topoisomerase I inhibitors. From both of these perspectives, mitotic kinesins are attractive targets for new anti-cancer agents.
Mitotic kinesins are enzymes essential for assembly and function of the mitotic spindle, but are not generally part of other microtubule structures such as nerve processes. Mitotic kinesins play essential roles during all phases of mitosis. These enzymes are “molecular motors” that transform energy released by hydrolysis of ATP into mechanical force which drives the directional movement of cellular cargoes along microtubules. The catalytic domain sufficient for this task is a compact structure of approximately 340 amino acids. During mitosis, kinesins organize microtubules into the bipolar structure that is the mitotic spindle. Kinesins mediate movement of chromosomes along spindle microtubules, as well as structural changes in the mitotic spindle associated with specific phases of mitosis. Experimental perturbation of mitotic kinesin function causes malformation or dysfunction of the mitotic spindle, frequently resulting in cell cycle arrest and cell death.
Among the identified mitotic kinesins is kinesin spindle protein (KSP). KSP belongs to an evolutionarily conserved kinesin subfamily of plus end-directed microtubule motors that assemble into bipolar homotetramers consisting of antiparallel homodimers. During mitosis, KSP associates with microtubules of the mitotic spindle. Microinjection of antibodies directed against KSP into human cells prevents spindle pole separation during prometaphase, giving rise to monopolar spindles and causing mitotic arrest and induction of programmed cell death. KSP and related kinesins in other non-human organisms bundle antiparallel microtubules and slide them relative to one another, thus forcing the spindle poles apart. KSP may also mediate in anaphase B spindle elongation and focusing of microtubules at the spindle pole.
Human KSP or HsEg5 has been described (Blangy, et al., Cell, 83:1159-69 (1995); Whitehead, et al., Arthritis Rheum., 39:1635-42 (1996); Galtio, et al., J. Cell Biol., 135:339-414 (1996); Blangy, et al., J. Bio. Chem., 272:19418-24 (1997); Blangy, et al., Cell Motil Cytoskeleton, 40:174-82 (1998); Whitehead and Rattner, J. Cell Sci., 111:2551-61 (1998); Kaiser, et al., JBC 274:18925-31 (1999); GenBank accession numbers: X85137, NM004523 and U37426), and a fragment of the KP gene (TRIPS) has been described (Lee, et al., Mol. Endocrinol., 9:243-54 (1995); GenBank accession number L40372). Xenopus KSP homologs (Eg5), as well as Drosophilia K-LP61 F/KRP 130 have been reported.
Small molecule inhibitors of KSP have recently been described in WO 03/079,973 and WO 2005/035512.
Mitotic kinesins are therefore attractive targets for the discovery and development of novel mitotic chemotherapeutics.